It is well known to utilize an elastomer seal in a hydraulic piston and cylinder assembly in a safety valve such as shown in U.S. Pat. Nos. 4,161,219 and 4,049,052. However, elastomer seals are limited as to the temperatures in which they can operate, the pressures which they can withstand, the corrosive environment in which they can operate, and the length of time before they must be replaced. Copending patent application Ser. No. 322,318 entitled Metal to Metal High/Low Pressure Seal, filed Nov. 17, 1981, discloses a metal-to-metal seal used in a piston and cylinder actuating assembly in a subsurface safety valve. However, it is difficult to manufacture metal-to-metal seals which will seal under all pressure conditions and which will seal against gases.
The present invention is directed to a hydraulic actuating means for actuating a subsurface well safety valve which avoids the use of elastomer seals and can be used in both high and low pressure and high and low temperature applications and in the presence of corrosive fluids and gases.